The present invention relates to multi-nozzle ink jet printing for divisional-printing or color-printing information on a same paper by use of a plurality of nozzles which are mounted on a carriage and eject ink of a same color or of different colors. More particularly, the present invention relates to a method of preventing images on the paper from being being unregisitered due to positional deviation between the ink issuing from the nozzles with respect to an intended direction of movement of the carriage.
In one type of prior art color ink jet printers, a plurality of ink ejection nozzles are mounted on a carriage and supplied respectively with ink of different colors so that monochromatic information may be reproduced by ink ejection from particular one of the nozzles or, alternatively, multi-color information by ink ejection from a plurality of nozzles. For example, a color ink jet printer disclosed in Japanese Patent Application No. 56-210743/1981 includes a charged drop detection electrode located ouside and adjacent to a side platen, which is loaded with a paper, and causes nozzles to sequentially face the detection electrode to thereby control ejected ink drops to a predetermined height. Such allows ink drops from the respective nozzles to share the same amount of deflection in a direction perpendicular to an intended direction of movement of the carriage, i.e. direction of ink drop deflection. Such deflection adjustment is adapted for the prevention of unregistered printing in the above-mentioned direction, e.g. deviation of colors in multi-color printing.
In the prior art ink jet printer discussed above, it sometimes occurs that the direction of ink ejection is shifted due to machining errors, assembling errors and others, or that upon operation of the printer after a several days of suspension the direction of ink ejection is shifted within a range of substantially .+-.100 microns owing to solidification of ink due to drying in the vicinity of the nozzles. So long as the shift or deviation of the ejection direction occurs in the direction of ink drop deflection, it is not causative of unregistered printing by virtue of compensation accomplished by the previously mentioned deflection adjustment. However, when the ejection direction of ink from one or more nozzles is shifted in the direction of movement of the carriage, compensation fails to be implemented by the deflection adjustment and color deviation is brought about in the carriage moving direction.
Such a problem is also encountered with a case wherein, in order to effect divisional-printing on a paper with respect to the deflection direction, a plurality of nozzles are arranged side by side along the direction of carriage movement and so set beforehand as to eject ink in different directions with respect to the ejection direction as well, the difference corresponding to a predetermined printing width. For example, as shown in FIGS. 1A and 1B, divisional-printing is accomplished by use of two nozzles N.sub.1 and N.sub.2 which are mounted on a carriage and shifted in position from each other in both the direction of carriage movement and the deflection direction. In FIGS. 1A and 1B, assume that upper half of a character A, for example, is printed out by the nozzle N.sub.1 which enters a predetermined printing zone first in response to the movement of the carriage, and lower half of the character A by the nozzle N.sub.2 which enters the printing zone with a delay associated with the positional deviation between the two nozzles with respect to the direction of carriage movement. Then, so long as the directions of ink ejection from the two nozzles N.sub.1 and N.sub.2 are normal, they will print out the character A in an orderly configuration as shown in FIG. 1A. However, should any of the nozzles be dislocated even a little in the direction of carriage movement, only a disfigured or unregistered character would be printed out as shown in FIG. 1B. Here, deviation in the deflection direction may be compensated by the previously discussed deflection adjustment.